It is a well known practice within dye diffusion thermal transfer printers that, in order to controllably drive the paper and maintain traction for precise image registration between color passes, an aggressively textured drive roller, and a companion pinch roller that applies a load between the paper and drive roller, is commonly used. This type of drive system does not result in any image artifacts on the printed paper when printing only on one side, or simplex printing, because the aggressively textured drive roller is not contacting the printed side of the paper. This method does present a problem when printing a two-sided, or duplex print because the aggressively textured drive roller must contact both sides of the printed sheet. For two-sided or duplex printing, the paper surface that is in contact with the aggressively textured surface of the drive roller may become compromised by the aggressively textured surface. This compromised paper surface may not receive dye transfer as readily, resulting in a visible density difference between the area of the paper that saw contact with the drive roller's aggressive texture and the area that did not contact the aggressive texture.
It is also common practice within the dye diffusion thermal transfer printer firmware to incorporate compensation algorithms that correct for across the page density variations, and/or down the page density variations. There may be limitations within the printer hardware or printer firmware such that compensation algorithms cannot completely compensate for printing artifacts generated by the drive roller. Due to these limitations, it becomes important to minimize the deviations in a print medium surface caused by the textured drive roller contacting the medium.
With respect to FIG. 1, for two-sided or duplex dye diffusion thermal transfer printing, a common method is to use two thermal print heads 102, 109, by first driving the rolled print medium 106 via drive roller (or capstan roller) 105 and pinch roller 104, in cooperation with a motor drive (not shown) on roll 106, to between platen roller 112 and one thermal print head 102 (print medium path of travel is shown in solid line), and printing on one side, Side A, of the print medium using dye donor 101. A length of print medium received from print medium roll 106 driven through the drive roller 105 and pinch roller 104 exposes Side B to come into contact with the drive roller's surface texture, compromising the Side B surface for subsequent printing. The Side B surface is compromised via the textured drive roller 105 perforating, forming depressions, pitting, or indenting the outermost layer, or more layers, of the Side B surface. The print media is then re-positioned by reversing drive roller 105 and pinch roller 104 in cooperation with the motor drive on roll 106, so that the lead edge of the paper is retracted toward the supply roll 106 and then diverted to the path represented by the dashed line. The rolled print medium 106 is driven via drive roller (or capstan roller) 105, pinch roller 107, in cooperation with the motor drive on roll 106, to between platen roller 111 and the second thermal print head 109. The non-printed surface, Side B, of the print medium is then printed using dye donor 110.